U.S. patent application number 14/002925 was filed with the patent office on 2014-01-02 for mobile terminal apparatus, radio base station apparatus and radio communication method.
This patent application is currently assigned to NTT DOCOMO, INC.. The applicant listed for this patent is Anass Benjebbour, Satoshi Nagata. Invention is credited to Anass Benjebbour, Satoshi Nagata.
Application Number | 20140003272 14/002925 |
Document ID | / |
Family ID | 46797977 |
Filed Date | 2014-01-02 |
United States Patent
Application |
20140003272 |
Kind Code |
A1 |
Benjebbour; Anass ; et
al. |
January 2, 2014 |
MOBILE TERMINAL APPARATUS, RADIO BASE STATION APPARATUS AND RADIO
COMMUNICATION METHOD
Abstract
To provide a mobile terminal apparatus, radio base station
apparatus and radio communication method that enable accurate
precoding weights to be generated in coordinated multipoint
transmission, a radio communication method of the invention is
characterized in that a mobile terminal apparatus (10) performs
channel estimation using a downlink reference signal, selects a PMI
using the obtained channel estimation value, measures an IQI using
at least the channel estimation value and the PMI, and transmits at
least the PMI and IQI to a radio base station apparatus, and that
the radio base station apparatus generates precoding weights using
the PMI and IQI, and performs coordinated multipoint transmission
utilizing MIMO transmission using the precoding weights.
Inventors: |
Benjebbour; Anass; (Tokyo,
JP) ; Nagata; Satoshi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Benjebbour; Anass
Nagata; Satoshi |
Tokyo
Tokyo |
|
JP
JP |
|
|
Assignee: |
NTT DOCOMO, INC.
Tokyo
JP
|
Family ID: |
46797977 |
Appl. No.: |
14/002925 |
Filed: |
February 21, 2012 |
PCT Filed: |
February 21, 2012 |
PCT NO: |
PCT/JP2012/054174 |
371 Date: |
September 3, 2013 |
Current U.S.
Class: |
370/252 ;
370/328 |
Current CPC
Class: |
H04B 7/0632 20130101;
H04B 7/0695 20130101; H04B 7/0639 20130101; H04J 11/0033 20130101;
H04L 25/03949 20130101; H04J 11/0053 20130101; H04B 7/0417
20130101; H04J 2211/005 20130101; H04B 7/024 20130101; H04B 7/0456
20130101 |
Class at
Publication: |
370/252 ;
370/328 |
International
Class: |
H04B 7/04 20060101
H04B007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2011 |
JP |
2011-047972 |
Claims
1. A mobile terminal apparatus comprising: a channel estimation
section configured to perform channel estimation using a downlink
reference signal; a PMI selecting section configured to select a
PMI (Precoding Matrix Indicator) using a channel estimation value
obtained in the channel estimation section; an IQI measuring
section configured to measure an IQI (Interference Quality
Indicator) using at least the channel estimation value and the PMI;
and a transmission section configured to transmit at least the PMI
and the IQI to a radio base station apparatus.
2. The mobile terminal apparatus according to claim 1, wherein the
IQI measuring section obtains the IQI using at least average
transmission power of each radio base station apparatus and a
quantization error on the mobile terminal apparatus side.
3. The mobile terminal apparatus according to claim 1, wherein the
IQI measuring section obtains the IQI using following equation (5):
IQI i j = P avg , j ICI i + N i + P avg , j .times. H i j - ( F i j
) H 2 , .A-inverted. i , j = 1 , 2 , 3 Eq . ( 5 ) ##EQU00015##
H.sub.i.sup.j: Downlink channel state; F.sub.i.sup.j: PMI feedback
from a mobile terminal apparatus i; P.sub.avg,j: Average total
transmission power of a radio base station apparatus j; ICI.sub.i:
Interference except interference from a cell belonging to a CoMP
set in the mobile terminal apparatus i; and N: Average noise.
4. The mobile terminal apparatus according to claim 1, wherein the
IQI measuring section obtains the IQI using following equation (9):
IQI i j = P avg , i ICI i + N i i = j IQI i j = P avg , j ICI i + N
i + P avg , j .times. H i j - ( F i j ) H 2 j .noteq. i Eq . ( 9 )
##EQU00016## H.sub.i.sup.j: Downlink channel state; F.sub.i.sup.j:
PMI feedback from a mobile terminal apparatus i; P.sub.avg,j:
Average total transmission power of a radio base station apparatus
j; ICI.sub.i: Interference except interference from a cell
belonging to a CoMP set in the mobile terminal apparatus i; and N:
Average noise.
5. The mobile terminal apparatus according to claim 1, wherein the
IQI measuring section obtains the IQI using following equation
(10): IQI i i = P avg , i ICI i + N i + P avg , i .times. H i i -
.lamda. i , max i ( F i i ) H 2 i = j IQI i j = P avg , j ICI i + N
i + P avg , j .times. H i j - ( F i j ) H 2 j .noteq. i .lamda. i ,
max i = max eigenvalue ( H i i ) Eq . ( 10 ) ##EQU00017##
H.sub.i.sup.j: Downlink channel state; F.sub.i.sup.j: PMI feedback
from a mobile terminal apparatus i; P.sub.avg,j: Average total
transmission power of a radio base station apparatus j; ICI.sub.i:
Interference except interference from a cell belonging to a CoMP
set in the mobile terminal apparatus i; and N.sub.i: Average noise
in a receiver in the mobile terminal apparatus i.
6. The mobile terminal apparatus according to claim 1, wherein the
IQI measuring section obtains a time-averaged IQI using following
equation (15): IQI i j = ( IQI i , avg j ) T + 1 = T + 1 T ( IQI i
, avg j ) T + 1 IQI i , T + 1 j Eq . ( 15 ) ##EQU00018##
(IQI.sub.i.sup.j).sub.T+1: Instantaneous value of IQI in a subframe
(T+1); (IQI.sub.i,avg.sup.j) .sub.T+1: Average value of IQI in a
subframe (T+1); and T+1; Length of a time window to average.
7. The mobile terminal apparatus according to claim 1, wherein the
IQI measuring section obtains a time-averaged IQI undergoing
weighting using following equation (16): IQI i j = ( IQI i , avg j
) T + 1 = 1 ( 1 - .alpha. ) ( IQI i , avg j ) T + .alpha. IQI i , T
+ 1 j 0 < .alpha. .ltoreq. 1 Eq . ( 16 ) ##EQU00019##
8. A radio base station apparatus comprising: a precoding weight
generating section configured to generate precoding weights using a
PMI (Precoding Matrix Indicator) and an IQI (Interference Quality
Indicator) transmitted from a mobile terminal apparatus as
feedback; and a transmission section configured to perform
coordinated multipoint transmission utilizing MIMO transmission
using the precoding weights.
9. The radio base station apparatus according to claim 8, further
comprising: an IQI processing section configured to obtain the IQI
using information necessary for IQI measurement including at least
a channel estimation value and the PMI from the mobile terminal
apparatus.
10. The radio base station apparatus according to claim 9, wherein
the IQI processing section obtains a time-averaged IQI using
following equation (15): IQI i j = ( IQI i , avg j ) T + 1 = T + 1
T ( IQI i , avg j ) + 1 IQI i , T + 1 j Eq . ( 15 ) ##EQU00020##
(IQI.sub.i.sup.j).sub.T+1: Instantaneous value of IQI in a subframe
(T+1); (IQI.sub.i,avg.sup.j).sub.T+1: Average value of IQI in a
subframe (T+1); and T+1: Length of a time window to average.
11. The radio base station apparatus according to claim 9, wherein
the IQI processing section obtains a time-averaged IQI undergoing
weighting using following equation (16): IQI i j = ( IQI i , avg j
) T + 1 = 1 ( 1 - .alpha. ) ( IQI i , avg j ) T + .alpha. IQI i , T
+ 1 j 0 < .alpha. .ltoreq. 1 Eq . ( 16 ) ##EQU00021##
12. A radio communication method comprising: in a mobile terminal
apparatus, performing channel estimation using a downlink reference
signal; selecting a PMI (Precoding Matrix Indicator) using the
obtained channel estimation value; measuring an IQI (Interference
Quality Indicator) using at least the channel estimation value and
the PMI; transmitting at least the PMI and the IQI to a radio base
station apparatus; in the radio base station apparatus, generating
precoding weights using the PMI and the IQI; and performing
coordinated multipoint transmission utilizing MIMO transmission
using the precoding weights.
13. The radio communication method according to claim 12, wherein
the IQI is obtained using at least average transmission power of
each radio base station apparatus and a quantization error on the
mobile terminal apparatus side.
14. The radio communication method according to claim 12, wherein
the IQI is obtained using following equation (5): IQI i j = P avg ,
j ICI i + N i + P avg , j .times. H i j - ( F i j ) H 2 ,
.A-inverted. i , j = 1 , 2 , 3 Eq . ( 5 ) ##EQU00022##
H.sub.i.sup.j: Downlink channel state; F.sub.i.sup.j: PMI feedback
from a mobile terminal apparatus i; P.sub.avg,j: Average total
transmission power of a radio base station apparatus j; ICI.sub.i:
Interference except interference from a cell belonging to a CoMP
set in the mobile terminal apparatus i; and N.sub.i: Average noise
in a receiver in the mobile terminal apparatus i.
15. The radio communication method according to claim 12, wherein
the IQI is obtained using following equation (9): IQI i j = P avg ,
i ICI i + N i i = j IQI i j = P avg , j ICI i + N i + P avg , j
.times. H i j - ( F i j ) H 2 j .noteq. i Eq . ( 9 ) ##EQU00023##
H.sub.i.sup.j: Downlink channel state; F.sub.i.sup.j: PMI feedback
from a mobile terminal apparatus i; P.sub.avg,j: Average total
transmission power of a radio base station apparatus j; ICI.sub.i:
Interference except interference from a cell belonging to a CoMP
set in the mobile terminal apparatus i; and N.sub.i: Average noise
in a receiver in the mobile terminal apparatus i.
16. The radio communication method according to claim 12, wherein
the IQI is obtained using following equation (10): IQI i i = P avg
, i ICI i + N i + P avg , i .times. H i i - .lamda. i , max i ( F i
i ) H 2 i = j IQI i j = P avg , j ICI i + N i + P avg , j .times. H
i j - ( F i j ) H 2 j .noteq. i .lamda. i , max i = max eigenvalue
( H i i ) Eq . ( 10 ) ##EQU00024## H.sub.i.sup.j: Downlink channel
state; H.sub.i.sup.j: PMI feedback from a mobile terminal apparatus
i; P.sub.avg,j: Average total transmission power of a radio base
station apparatus j; ICI.sub.i: Interference except interference
from a cell belonging to a CoMP set in the mobile terminal
apparatus i; and N.sub.i: Average noise in a receiver in the mobile
terminal apparatus i.
17. A radio communication method comprising: in a mobile terminal
apparatus, performing channel estimation using a downlink reference
signal; selecting a PMI (Precoding Matrix Indicator) using the
obtained channel estimation value; measuring an IQI (Interference
Quality Indicator) using at least the channel estimation value and
the PMI; transmitting at least the PMI and the IQI to a radio base
station apparatus; in the radio base station apparatus, exchanging
the PMI and an IQI transmitted as feedback to each radio base
station apparatus included in a coordinated cluster between radio
base station apparatuses; generating precoding weights using PMIs
and IQIs of the radio base station and a coordinated base station
in each radio base station apparatus in the coordinated cluster;
and performing coordinated multipoint transmission utilizing MIMO
transmission using the precoding weights.
Description
TECHNICAL FIELD
[0001] The present invention relates to a mobile terminal
apparatus, radio base station apparatus, and radio communication
method, and more particularly, to a mobile terminal apparatus,
radio base station apparatus, and radio communication method that
support multi-antenna transmission.
BACKGROUND ART
[0002] In UMTS (Universal Mobile Telecommunications System)
networks, for the purpose of improving spectral efficiency and
further improving data rates, by adopting HSDPA (High Speed
Downlink Packet Access) and HSUPA (High Speed Uplink Packet
Access), it is performed exploiting maximum features of the system
based on W-CDMA (Wideband Code Division Multiple Access). For the
UMTS network, for the purpose of further increasing high-speed data
rates, providing low delay and the like, Long Term Evolution (LTE)
has been studied.
[0003] In the 3G system, a fixed band of 5 MHz is substantially
used, and it is possible to achieve transmission rates of
approximately maximum 2 Mbps in downlink. Meanwhile, in the
LTE-scheme system, using variable bands ranging from 1.4 MHz to 20
MHz, it is possible to achieve transmission rates of maximum 300
Mbps in downlink and about 75 Mbps in uplink. Further, in the UMTS
network, for the purpose of further increasing the wide-band and
high speed, successor systems to LTE have been studied (for
example, LTE Advanced (LTE-A)). For example, in LTE-A, it is
scheduled to increase 20 MHz that is the maximum system band in LTE
specifications to about 100 MHz.
[0004] Meanwhile, in the LTE-scheme system, MIMO (Multi Input Multi
Output) systems are proposed as radio communication techniques for
transmitting and receiving data using a plurality of antennas and
improving a data rate (spectral efficiency) (for example, see
Non-patent Document 1). In the MIMO systems, the
transmitter/receiver is provided with a plurality of
transmission/reception antennas, and simultaneously transmits
different transmission information sequences from different
transmission antennas. Meanwhile, the receiver side exploits the
fact that different fading variations occur in between transmission
and reception antennas, and divides the simultaneously-transmitted
information sequences to detect, and it is thereby possible to
increase the data rate (spectral efficiency).
[0005] In the LTE-scheme system, specified are Single User MIMO
(SU-MIMO) transmission in which transmission information sequences
simultaneously transmitted from different transmission antennas are
all for the same user and Multiple User MIMO (MU-MIMO) transmission
in which the transmission information sequences are for different
users. In the SU-MIMO transmission and MU-MIMO transmission, the
receiver side selects an optimal PMI (Precoding Matrix Indicator)
from a codebook that defines a plurality of phase/amplitude control
amounts (precoding matrixes (precoding weights)) to set on antennas
of the transmitter and PMIs associated with the precoding matrixes,
and transmits the PMI to the transmitter as feedback. The
transmitter side performs precoding on each transmission antenna
based on the PMI that is transmitted from the receiver as feedback,
and transmits transmission information sequences. As typical
precoding techniques, there are ZF (Zero Forcing), BD (Block
Diagonalization) ZF, MMSE (Minimum Mean Square Error), SLNR (Signal
to Leakage plus Noise Ratio), etc.
[0006] Herein, attention is directed toward SLNR precoding. In SLNR
precoding, a value is maximized which is obtained by dividing power
of a desired signal received in a receiver (herein, mobile terminal
apparatus) by the sum of interference caused by "leakage" of a
signal in another mobile terminal apparatus in the coordinated
cluster, noise and all power. In calculating precoding weights by
SLNR precoding, the need arises for an average reception SINR
(Signal to Interference plus Noise Ratio) in the mobile terminal
apparatus (for example, see Non-patent Document 2).
CITATION LIST
Non-Patent Literature
[0007] [Non-Patent Literature 1] 3GPP TR 25.913 "Requirements for
Evolved UTRA and Evolved UTRAN" [0008] [Non-Patent Literature 2] M.
Sadek et al., "A leakage-based precoding scheme for downlink
multi-user MIMO channels," IEEE Trans. Wireless Commun., vol. 6,
no. 5, pp. 1713, May 2007.
[0009] As one of promising techniques to further improve system
performance of Rel-8 LTE system, there is inter-cell
orthogonalization. In LTE systems of Rel-10 or later (LTE-A
system), intra-cell orthogonalization is achieved by orthogonal
multiple access both in uplink and downlink. In other words, in
downlink, mobile terminal apparatuses (User Equipments) are
orthogonalized in the frequency domain. However, for inter-cell,
interference randomizing by 1-cell frequency reuse is a base as in
W-CDMA. The 3GPP (3rd Generation Partnership Project) has studied
Coordinated Multipoint (CoMP) transmission/reception as techniques
for actualizing inter-cell orthogonalization. In CoMP
transmission/reception, a plurality of cells coordinates to perform
signal processing of transmission and reception on a single or a
plurality of mobile terminal apparatuses (UEs). More specifically,
studied in downlink are multi-cell simultaneous transmission
applying precoding, coordinated scheduling/beamforming and the
like.
[0010] In the case of applying downlink coordinated
scheduling/beamforming transmission using SLNR precoding, by using
instantaneous channel quality information CQI (Channel Quality
Indicator) and PMI that are transmitted from the mobile terminal
apparatus to the radio base station apparatus as feedback, an
average reception SINR is calculated using the instantaneous CQI
(following equations (1) and (2)).
CQI feedback from a mobile terminal apparatus i CQI i j = H i j F i
j 2 .times. P avg , j ICI i + N i Eq . ( 1 ) ##EQU00001##
[0011] i,j: 1, 2, . . . (numbers of mobile terminal apparatus i and
radio base station apparatus j)
[0012] H.sub.i.sup.j: Downlink channel state between the radio base
station apparatus j and mobile terminal apparatus i
[0013] F.sub.i.sup.j: PMI feedback from the mobile terminal
apparatus i
[0014] P.sub.avg,j: Average total transmission power from the radio
base station apparatus j
[0015] ICI.sub.i: Interference from a cell that does not belong to
a CoMP set in the mobile terminal apparatus i
[0016] N.sub.i: Average noise of a receiver in the mobile terminal
apparatus i
[0017] Herein, since the mobile terminal apparatus i is connected
to the radio base station apparatus i, the radio base station
apparatus i is called the serving base station of the mobile
terminal apparatus i, and another radio base station apparatus
j.noteq.i in the cluster is called the coordinating base
station.
CQI i j i j = H i j F i j 2 .times. P avg , j ICI i + N i Eq . ( 2
) ##EQU00002##
[0018] However, the transmission power component in the numerator
of above-mentioned equation (1) is not a value averaged in the time
domain, and is an instantaneous value. Further, in the
instantaneous CQI used as the average reception SINR, a
quantization error (deviation from the desired beam direction) is
not considered. Therefore, when SLNR precoding is performed using
an instantaneous CQI as the average reception SINR, it is not
possible to generate accurate precoding weights.
SUMMARY OF THE INVENTION
[0019] The present invention was made in view of such a respect,
and it is an object of the invention to provide a mobile terminal
apparatus, radio base station apparatus and radio communication
method that enable accurate precoding weights to be generated in
coordinated multipoint (CoMP) transmission.
[0020] A mobile terminal apparatus of the invention is
characterized by having a channel estimation section configured to
perform channel estimation using a downlink reference signal, a PMI
selecting section configured to select a PMI using a channel
estimation value obtained in the channel estimation section, an IQI
measuring section configured to measure an IQI (Interference
Quality Indicator) using at least the channel estimation value and
the PMI, and a transmission section configured to transmit at least
the PMI and the IQI to a radio base station apparatus.
[0021] A radio base station apparatus of the invention is
characterized by having a preceding weight generating section
configured to generate preceding weights using a PMI and IQI
transmitted from a mobile terminal apparatus as feedback, and a
transmission section configured to perform coordinated multipoint
transmission utilizing MIMO transmission using the precoding
weights.
[0022] A radio communication method of the invention is
characterized by having the steps in a mobile terminal apparatus of
performing channel estimation using a downlink reference signal,
selecting a PMI using the obtained channel estimation value,
measuring an IQI using at least the channel estimation value and
the PMI, and transmitting at least the PMI and the IQI to a radio
base station apparatus, and the steps in the radio base station
apparatus of generating precoding weights using the PMI and the IQI
transmitted from the mobile terminal apparatus as feedback, and
performing coordinated multipoint transmission utilizing MIMO
transmission using the preceding weights. In addition, in the
present invention, to calculate SLNR preceding, as well as the PMI,
IQIs may be exchanged between radio base station apparatuses in a
coordinated cluster (in a CoMP set).
[0023] According to the invention, the mobile terminal apparatus
measures an IQI using at least a channel estimation value and PMI,
and the radio base station apparatus generates precoding weights
using the PMI and IQI, performs coordinated multipoint transmission
utilizing MIMO transmission using the precoding weights, and
therefore, in MIMO transmission of coordinated multipoint
transmission, is capable of performing accurate SLNR precoding
using, as an average reception SINR, the IQI with consideration
given to average transmission power from each radio base station
and instantaneous quantization error in the mobile terminal
apparatus.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a diagram to explain CS/CB type CoMP;
[0025] FIG. 2 is a diagram to explain MIMO transmission;
[0026] FIG. 3 is a diagram to explain a configuration of a mobile
communication system according to one Embodiment of the
invention;
[0027] FIG. 4 is a block diagram illustrating a configuration of a
mobile terminal apparatus according to the above-mentioned
Embodiment; and
[0028] FIG. 5 is a block diagram illustrating a configuration of a
radio base station apparatus according to the above-mentioned
Embodiment.
DESCRIPTION OF EMBODIMENTS
[0029] Downlink CoMP transmission will be described first. As
downlink CoMP transmission, there are Coordinated
Scheduling/Coordinated Beamforming (CS/CB) and Joint processing. As
shown in FIG. 1, Coordinated scheduling/Coordinated beamforming is
a method in which only one cell transmits to one UE, and radio
resources in the frequency/spatial domain are allocated with
consideration given to interference from another cell and
interference to another cell. Meanwhile, Joint processing is
simultaneous transmission of a plurality of cells to which
precoding is applied, and has Joint transmission in which a
plurality of cells transmits to one UE, and Dynamic Cell Selection
in which a cell is instantaneously selected.
[0030] MIMO techniques will be described next.
[0031] In precoding in downlink MIND transmission of a MIND system
as shown in FIG. 2, a mobile terminal apparatus UE measures a
channel coefficient using a reception signal from each antenna, and
based on the measured channel coefficient, selects a PMI and RI
(Rank Indicator), from a precoding codebook, corresponding to phase
and amplitude control amounts (precoding weights) that maximize
throughput subsequent to combining transmission data from
respective transmission antennas of a radio base station apparatus
eNB. Then, the UE transmits the selected PMI and RI to the radio
base station apparatus eNB together with channel quality
information CQI as feedback. The radio base station apparatus eNB
performs channel coding and data modulation (AMC: Adaptive
Modulation and Coding) on a transmission signal, and performs
precoding on transmission data based on the PMI and RI transmitted
from the mobile terminal apparatus (UE) as feedback. By this means,
the phase and amplitude is respectively controlled (shifted) for
each transmission antenna. Then, the eNB transmits the transmission
data with the phase and amplitude shifted from each antenna.
[0032] In CS/CB type CoMP transmission, in performing SLNR
precoding, when an instantaneous CQI is used as an average
reception SINR, as described above, since the transmission power
component of the numerator of above-mentioned equation (1) is not
an average and instantaneous and a quantization error is not
considered in an instantaneous CQI, it is not possible to generate
accurate precoding weights.
[0033] Therefore, the inventors of the present invention found out
that it is possible to generate accurate precoding weights by
defining new feedback information that includes an average
transmission power component and that corrects a quantization
error, and performing SLNR precoding using the feedback
information, and arrived at the invention.
[0034] In other words, it is the gist of the invention measuring an
IQI using at least a channel estimation value and PMI, generating
precoding weights using the PMI and IQI, performing coordinated
multipoint transmission utilizing MIMO transmission using the
precoding weights, and in MIMO transmission of coordinated
multipoint transmission, thereby performing accurate SLNR precoding
using the IQI with consideration given to the average transmission
power from each radio base station and the quantization error on
the mobile terminal apparatus side.
[0035] In the invention, to generate accurate precoding weights, a
new interference quality indicator (IQI: Interference Quality
Indicator) is defined in SLNR precoding. Accordingly, in the
invention, in downlink coordinated multipoint transmission, a
mobile terminal apparatus transmits the IQI to a radio base station
apparatus as feedback in addition to the PMI and CQI as feedback
information.
[0036] The IQI is calculated as described in following equation
(3). Further, a reception signal y.sub.i in a mobile terminal
apparatus is calculated from a desired signal component and an
interference signal component including a quantization error and
noise as described in following equation (4).
IQI i j = P j ICI i + N i + QE i , j , .A-inverted. i , j .di-elect
cons. In CoMP SET Eq . ( 3 ) ##EQU00003##
[0037] P.sub.j: Average transmission power of a radio base station
apparatus j
[0038] QE.sub.i,j: Quantization error of a channel between the
radio base station apparatus j and a mobile terminal apparatus i in
the mobile terminal apparatus i
[0039] ICI.sub.i: Interference except interference from a cell
belonging to a CoMP set in the mobile terminal apparatus i
[0040] N.sub.i: Average noise in a receiver in the mobile terminal
apparatus i
y i = H i j s j + n i = ( F i j ) H s j DESIRED SIGNAL COMPONENT +
( H i j - ( F i j ) H ) s j + ICI i + n i INTERFERENCE SIGNAL
COMPONENT INCLUDING QUANTIZATION ERROR AND NOISE Eq . ( 4 )
##EQU00004##
[0041] H.sub.i.sup.j: Downlink channel state
[0042] F.sub.i.sup.j: PMI feedback from the mobile terminal
apparatus i
[0043] In the invention, the IQI that is specific feedback
information is defined in five aspects.
(Aspect 1)
[0044] In this Aspect, the IQI is defined by following equation
(5).
IQI i j = P avg , j ICI i + N i + P avg , j .times. H i j - ( F i j
) H 2 , .A-inverted. i , j Eq . ( 5 ) ##EQU00005##
[0045] P.sub.avg,j: Average total transmission power of the radio
base station apparatus j
[0046] In above-mentioned equation (5), the numerator P.sub.avg,j
represents average transmission power, ICI.sub.i+N.sub.i represents
interference+average noise from another cell (cell except the CoMP
set) on the mobile terminal apparatus side, and
P.sub.avg,j.times.//H.sub.i.sup.j-(F.sub.i.sup.j).sup.H//.sup.2
represents a quantization error.
[0047] Thus, the calculation equation of the IQI includes the terms
of average transmission power from each radio base station and the
quantization error on the mobile terminal apparatus side, and
therefore, the IQI is a parameter considering both. The radio base
station apparatus performs SLNR precoding using the IQI, and is
thereby capable of generating accurate precoding weights.
[0048] In addition, in above-mentioned equation (5), instead of
H.sub.i.sup.j, normalized H.sub.i.sup.j may be used which is
normalized by norm as in following equation (6).
H _ i j = H i j H i j Eq . ( 6 ) ##EQU00006##
[0049] Further, for the IQI, instead of above-mentioned equation
(5), following equation (7) may be used. In addition, F.sub.i.sup.j
is a vector of norm 1 as shown in following equation (8).
IQI i j = P avg , j ICI i + N i + P avg , j .times. H i j F i j - I
2 , .A-inverted. i , j Eq . ( 7 ) ##EQU00007##
[0050] In addition, descriptions of the same parameters as in the
above-mentioned equations are the same, and are omitted.
F.sub.i.sup.j(F.sub.i.sup.j).sup.H=I Eq. (8)
[0051] In this Aspect, the definitions of the IQI are not limited
to above-mentioned equations (5) and (7), and it is possible to
apply all substantially equivalent equations by conversion of the
equation and the like.
(Aspect 2)
[0052] In this Aspect, the IQI is defined by following equation
(9). In this Aspect, the IQI for the connected cell (serving cell)
(eNB.sub.1 in FIG. 1) and the IQI for the coordinated cell
(eNB.sub.2 in FIG. 1) are defined independently. In other words, in
calculation of the IQI, for the connected cell, the quantization
error is regarded as being small, and is not considered in the IQI
calculation equation of the connected cell, and the quantization
error is considered only for the coordinated cell.
IQI i j = P avg , i ICI i + N i i = j IQI i j = P avg , j ICI i + N
i + P avg , j .times. H i j - ( F i j ) H 2 j .noteq. i Eq . ( 9 )
##EQU00008##
[0053] In addition, descriptions of the same parameters as in the
above-mentioned equations are the same, and are omitted.
[0054] Thus, the calculation equation of the IQI includes the terms
of average transmission power from each radio base station and the
quantization error on the mobile terminal apparatus side, and
therefore, the IQI is a parameter considering both. The radio base
station apparatus performs SLNR precoding using the IQI, and is
thereby capable of generating accurate precoding weights. In this
case, since the quantization error is not considered for the
connected cell, it is possible to reduce the IQI calculation
amount. In addition, in this Aspect, the definitions of the IQI are
not limited to above-mentioned equation (9), and it is possible to
apply all substantially equivalent equations by conversion of the
equation and the like.
(Aspect 3)
[0055] In this Aspect, the IQI is defined by following equation
(10). Also in this Aspect, the IQI for the connected cell (serving
cell) (eNB.sub.1 in FIG. 1) and the IQI for the coordinated cell
(eNB.sub.2 in FIG. 1) are defined independently. In other words, in
calculation of the IQI, in considering the quantization error, for
the connected cell, since the quantization error is small, a weight
of the quantization error is reduced. More specifically, for the
connected cell, used is a maximum value of the eigenvalue by eigen
decomposition of the channel matrix H.sub.i.sup.i.
IQI i j = P avg , i ICI i + N i + P avg , i .times. H i i - .lamda.
i , max i ( F i i ) H 2 i = j IQI i j = P avg , i ICI i + N i + P
avg , j .times. H i j - ( F i j ) H 2 j .noteq. i .lamda. i , max i
= max eigenvalue ( H i i ) Eq . ( 10 ) ##EQU00009##
[0056] In addition, descriptions of the same parameters as in the
above-mentioned equations are the same, and are omitted.
(Aspect 4)
[0057] In this Aspect, in calculation of the IQI, in considering
the quantization error as defined in following equation (11),
weights of the quantization error are reduced for the connected
cell and coordinated cell. More specifically, the maximum value of
the eigenvalue by eigen decomposition is used for the connected
cell and coordinated cell.
IQI i j = P avg , j ICI i + N i + P avg , j .times. H i j - .lamda.
i , max j ( F i j ) H 2 .lamda. i , max j = max eigenvalue ( H i j
) Eq . ( 11 ) ##EQU00010##
[0058] In addition, descriptions of the same parameters as in the
above-mentioned equations are the same, and are omitted.
(Aspect 5)
[0059] In this Aspect, an instantaneous quantization error is not
considered for all of the connected cell and coordinated cell.
IQI i j = P avg , j ICI i + N i , .A-inverted. i , j Eq . ( 12 )
##EQU00011##
[0060] Thus, the calculation equation of the IQI includes the terms
of average transmission power and the quantization error on the
mobile terminal apparatus side, and therefore, the IQI is a
parameter considering both. The radio base station apparatus
performs SLNR precoding using the IQI, and is thereby capable of
generating accurate precoding weights. In this case, since the
quantization error is calculated by varying weights for the
connected cell and coordinated cell, it is possible to calculate
the quantization error more accurately. In addition, in this
Aspect, the definition of the IQI is not limited to above-mentioned
equation (10), and it is possible to apply all substantially
equivalent equations by conversion of the equation and the
like.
[0061] As an IQI feedback method, the mobile terminal apparatus may
calculate an IQI using a downlink reference signal, and transmit
the calculated IQI to the radio base station apparatus in uplink
(first feedback method). Alternatively, the mobile terminal
apparatus may obtain a part of a value (value capable of being
calculated only in the mobile terminal apparatus) required for
calculation of an IQI (calculation value of the denominator in
above-mentioned equation (5), (7), (9), (10, or (11):
IQI.sub.i,UE.sup.j) and transmit the obtained calculation value to
the radio base station apparatus in uplink, and the radio base
station apparatus may calculate the IQI using the calculation value
(second feedback method). By adopting such a latter feedback
method, it is possible to reduce the feedback information
amount.
[0062] In such a latter feedback method, for example, in Aspect 1,
the calculation value IQI.sub.i,UE.sup.j that the mobile terminal
apparatus transmits as feedback is a value shown in following
equation (13). The mobile terminal apparatus transmits this
calculation value IQI.sub.i,UE.sup.j to the radio base station
apparatus. The radio base station apparatus knows average total
transmission power (P.sub.avg,j) of the radio base station
apparatus j (by information exchange between radio base station
apparatuses in the cluster, or the like), and therefore, obtains
IQI.sub.i,eNB.sup.j=IQI.sub.i.sup.j using this parameter (following
equation (14)).
IQI i , UE j = ICI i + N i + P avg , j .times. H i j - ( F i j ) H
2 , .A-inverted. i , j Eq . ( 13 ) IQI i j = IQI i , eNB j = P avg
, j IQI i , UE j , .A-inverted. i , j Eq . ( 14 ) ##EQU00012##
[0063] Similarly, in Aspect 2, the calculation value
IQI.sub.i,UE.sup.j that the mobile terminal apparatus transmits as
feedback is a value calculated in the denominator of
above-mentioned equation (9). The mobile terminal apparatus
transmits this calculation value IQI.sub.i,UE.sup.j (connected cell
and coordinated cell) to the radio base station apparatus. The
radio base station apparatus i knows average total transmission
power (P.sub.avg,j) of the radio base station apparatus j, and
therefore, obtains IQI.sub.i,eNB.sup.j=IQI.sub.i.sup.j using this
parameter. Further, similarly, in Aspect 3, the calculation value
IQI.sub.i,UE.sup.j that the mobile terminal apparatus transmits as
feedback is a value calculated in the denominator of
above-mentioned equation (10). The mobile terminal apparatus
transmits this calculation value IQI.sub.i,UE.sup.j (connected cell
and coordinated cell) to the radio base station apparatus. The
radio base station apparatus i knows average total transmission
power (P.sub.avg,j) of the radio base station apparatus j, and
therefore, obtains IQI.sub.i,eNB.sup.j=IQI.sub.i.sup.j using this
parameter.
[0064] In above-mentioned Aspects 1 to 5, an instantaneous value is
used in calculation of the IQI with the quantization error
considered. In the case of generating precoding weights using the
IQI, it is desirable to time-average the IQI value so as to further
improve accuracy. More specifically, as shown in following equation
(15), the mobile terminal apparatus obtains an average value (time
average value) of the IQI at time T+1, using an average value of
the IQI at time T and IQI instantaneous value at time T+1, and
transmits the time average value to the radio base station
apparatus as feedback.
IQI i j = ( IQI i , avg j ) T + 1 = T + 1 T ( IQI i , avg j ) + 1
IQI i , T + 1 j Eq . ( 15 ) ##EQU00013##
[0065] (IQI.sub.i.sup.j).sub.T+1: Instantaneous value of IQI in a
subframe (T+1)
[0066] (IQI.sub.i,avg.sup.j).sub.T+1: Average value of IQI in a
subframe (T+1)
[0067] T+1: Length of the averaging time window
[0068] For time-averaging of the IQI, the mobile terminal apparatus
side may perform, or the radio base station apparatus side may
perform. In other words, the mobile terminal apparatus may obtain
an IQI instantaneous value, and transmit this IQI instantaneous
value to the radio base station apparatus as feedback, and the
radio base station apparatus may time-average the IQI as shown in
above-mentioned equation (15). In addition, generally, a time
average interval of the IQI is longer than a time average interval
of the CQI.
[0069] Further, as shown in following equation (16), averaging may
be performed by providing the IQI instantaneous value at time T+1
and IQI average value at time T with weights. In this case, when
the weight of the instantaneous value is made higher than that of
the average value, the weight of the IQI instantaneous value at
time T+1 is increased. When the weight of the average value is made
higher than that of the instantaneous value, the weight of the IQI
average value at time T is increased. By this means, it is possible
to vary a value of .alpha. and adjust weighing on the instantaneous
value and average value.
IQI i j = ( IQI i , avg j ) T + 1 = 1 ( 1 - .alpha. ) ( IQI i , avg
j ) T + .alpha. IQI i , T + 1 j 0 < .alpha. .ltoreq. 1 Eq . ( 16
) ##EQU00014##
[0070] Thus, by time-averaging the IQI, it is possible to improve
IQI calculation accuracy, and improve accuracy of SLNR precoding
weights.
[0071] An Embodiment of the present invention will specifically be
described below with reference to accompanying drawings. Described
herein is the case of using the radio base station apparatus and
mobile terminal apparatus that support the LTE-A system.
[0072] Referring to FIG. 3, described is a mobile communication
system 1 having mobile terminal apparatuses (UEs: User Equipments)
10 and radio base station apparatus (eNode B) 20 according to one
Embodiment of the invention. FIG. 3 is a diagram to explain a
configuration of the mobile communication system 1 having mobile
terminal apparatuses 10 and radio base station apparatus 20
according to the Embodiment of the invention. In addition, for
example, the mobile communication system 1 as shown in FIG. 3 is a
system including the LTE system or Super 3G. Further, the mobile
communication system 1 may be called IMT-Advanced or may be called
4G.
[0073] As shown in FIG. 3, the mobile communication system 1
includes the radio base station apparatus 20 and a plurality of
mobile terminal apparatuses 10 (10.sub.1, 10.sub.2, 10.sub.3, . . .
10.sub.n, n is an integer where n.quadrature.0) that communicate
with the radio base station apparatus 20, and is comprised thereof.
The radio base station apparatus 20 is connected to an upper
station apparatus 30, and the upper station apparatus 30 is
connected to a core network 40. The mobile terminal apparatuses 10
communicate with the radio base station apparatus 20 in a cell 50.
In addition, for example, the upper station apparatus 30 includes
an access gateway apparatus, Radio Network Controller (RNC),
Mobility Management Entity (MME) and the like, but is not limited
thereto.
[0074] Each of the mobile terminal apparatuses (10.sub.1, 10.sub.2,
10.sub.3, . . . 10.sub.n) has the same configuration, function and
state, and is described as a mobile terminal apparatus 10 unless
otherwise specified in the following description. Further, for
convenience in description, the description is given while assuming
that equipment which performs radio communications with the radio
base station apparatus 20 is the mobile terminal apparatus 10, and
more generally, the equipment may be user equipment (UE) including
mobile terminal apparatuses and fixed terminal apparatuses.
[0075] In the mobile communication system 1, as a radio access
scheme, OFDMA (Orthogonal Frequency Division Multiple Access) is
applied in downlink, while SC-FDMA (Single-Carrier Frequency
Division Multiple Access) is applied in uplink. OFDMA is a
multicarrier transmission scheme for dividing a frequency band into
a plurality of narrow frequency bands (subcarriers), and mapping
data to each subcarrier to perform communications. SC-FDMA is a
single-carrier transmission scheme for dividing the system band
into bands comprised of a single or consecutive resource blocks for
each terminal so that a plurality of terminals uses mutually
different bands, and thereby reducing interference among the
terminals.
[0076] Described herein are communication channels in the LTE
system. In downlink, used are the PDSCH shared among the mobile
terminal apparatuses 10, and downlink L1/L2 control channels
(PDCCH, PCFICH, PHICH). User data i.e. normal data signals are
transmitted on the PDSCH. The transmission data is included in the
user data. In addition, a CC assigned to the mobile terminal
apparatus 10 in the radio base station apparatus 20 and scheduling
information is notified to the mobile terminal apparatus 10 on the
L1/L2 control channel.
[0077] In uplink, used are the PUSCH (Physical Uplink Shared
Channel) shared among the mobile terminal apparatuses 10, and the
PUCCH (Physical Uplink Control Channel) that is a control channel
in uplink. User data is transmitted on the PUSCH. Meanwhile, radio
quality information (CQI: Channel Quality Indicator) in downlink
and the like are transmitted on the PUCCH.
[0078] FIG. 4 is a block diagram illustrating a configuration of
the mobile terminal apparatus 10 according to this Embodiment. FIG.
5 is a block diagram illustrating a configuration of the radio base
station apparatus 20 according to this Embodiment. In addition, the
configurations of the mobile terminal apparatus 10 and the radio
base station apparatus 20 as shown in FIGS. 4 and 5 are simplified
to explain the present invention, and are assumed to have the
configurations that a normal mobile terminal apparatus and radio
base station apparatus have, respectively.
[0079] In the mobile terminal apparatus 10 as shown in FIG. 4,
transmission signals transmitted from the radio base station
apparatus 20 are received in reception antennas RX#1 to RX#N,
electrically divided into transmission paths and reception paths in
duplexers 101#1 to 101#N, and then, output to RF reception circuits
102#1 to 102#N. Then, the signals undergo frequency conversion
processing for converting a radio-frequency signal into a baseband
signal in the RF reception circuits 102#1 to 102#N. CPs are removed
from the baseband signals subjected to the frequency conversion
processing in cyclic prefix (CP) removing sections 103#1 to 103#N,
and the resultants are output to Fast Fourier Transform sections
(FFT sections) 104#1 to 104#N. A reception timing estimation
section 105 estimates reception timing from reference signals
included in the reception signals, and notifies the CP removing
sections 103#1 to 103#N of the estimation result. The FFT sections
104#1 to 104#N perform Fourier transform on the input reception
signals, and transform the time-series signals into signals in the
frequency domain. The reception signals transformed into the
signals in the frequency domain are output to a data channel signal
demodulation section 106.
[0080] The data channel signal demodulation section 106 divides the
reception signals input from the FFT sections 104#1 to 104#N, for
example, by Minimum Mean Square Error (MMSE) or Maximum Likelihood
Detection (MLD) signal division method. By this means, the
reception signals coming from the radio base station apparatus 20
are divided into reception signals concerning users #1 to #k, and a
reception signal concerning a user (herein, assumed to be a user k)
of the mobile terminal apparatus 10 is extracted. A channel
estimation section 107 estimates channel states from the reference
signals included in the reception signals output from the FFT
sections 104#1 to 104#N, and notifies the estimated channel states
to the data channel signal demodulation section 106, and a channel
quality measuring section 110 and PMI selecting section 111,
described later. The data channel signal demodulation section 106
divides the reception signals by the above-mentioned MLD signal
division method based on the notified channel states. By this
means, the reception signal concerning the user k is
demodulated.
[0081] In addition, it is assumed that the extracted reception
signal concerning the user k is demapped in a subcarrier demapping
section, not shown, and is restored to the time-series signal prior
to the demodulation processing in the data channel signal
demodulation section 106. The reception signal concerning the user
k demodulated in the data channel signal demodulation section 106
is output to a channel decoding section 108. Then, the channel
decoding section 108 performs channel decoding processing, and a
transmission signal #k is thus reproduced.
[0082] An IQI measuring section 109 measures an IQI using at least
the channel states (channel estimation values) notified from the
channel estimation section 107 and the PMI selected in the PMI
selecting section 111, described later. In other words, the IQI
measuring section 109 obtains the IQI by the above-mentioned
equations, using at least average transmission power of each radio
base station apparatus and the quantization error on the mobile
terminal apparatus side. For example, in Aspect 1, the section 109
calculates the IQI Of the connected cell and the IQI of the
coordinated cell by above-mentioned equation (5) or (7). Further,
in Aspect 2, the section 109 calculates the IQI Of the connected
cell and the IQI of the coordinated cell by above-mentioned
equation (9). In Aspect 3, the section 109 calculates the IQI Of
the connected cell and the IQI of the coordinated cell by
above-mentioned equation (10). In Aspect 4, the section 109
calculates the IQI Of the connected cell and the IQI of the
coordinated cell by above-mentioned equation (11).
[0083] In the above-mentioned first feedback method, the IQI
measuring section 109 calculates the IQI by above-mentioned
equation (5), (7), (9), (10) or (11) using at least the channel
states and PMI. In the above-mentioned second feedback method, the
section 109 calculates the calculation value (IQI.sub.i,UE.sup.j)
of the denominator of above-mentioned equation (5), (7), (9), (10)
or (11) using at least the channel states and PMI. The IQI
measuring section 109 outputs the calculated IQI or
IQI.sub.i,UE.sup.j to a feedback control signal generating section
112. Further, when necessary, the IQI measuring section 109
time-averages the IQI by above-mentioned equations (15) and
(16).
[0084] The channel quality measuring section 110 measures channel
quality (CQI) based on the channel states notified from the channel
estimation section 107. Then, the section 110 outputs the CQI that
is a measurement result to a feedback control signal generating
section 112. The PMI selecting section 111 selects a PMI based on
the channel states notified from the channel estimation section
107. Then, the section 111 outputs the selected PMI to the feedback
control signal generating section 112.
[0085] Using the IQI or IQI.sub.i,UE.sup.j from the IQI measuring
section 109, the CQI from the channel quality measuring section 110
and the PMI from the PMI selecting section 111, the feedback
control signal generating section 112 generates a control signal
(for example, PUCCH) to transmit the indicators to the radio base
station apparatus 20 as feedback. The control signal generated in
the feedback control signal generating section 112 is output to a
multiplexer (MUX) 117.
[0086] Transmission data #k concerning the user #k output from a
higher layer is subjected to channel coding in a channel coding
section 113, and is subjected to data modulation in a data
modulation section 114. The transmission data #k subjected to data
modulation in the data modulation section 114 is transformed from
the time-series signal into the signal in the frequency domain in a
serial/parallel transform section, not shown, and is output to a
subcarrier mapping section 115.
[0087] The subcarrier mapping section 115 maps the transmission
data #k to subcarriers corresponding to scheduling information
indicated from the radio base station apparatus 20. At this point,
the subcarrier mapping section 115 maps (multiplexes) a reference
signal #k generated in a reference signal generating section, not
shown, to the subcarriers together with the transmission data #k.
The transmission data #k thus mapped to the subcarriers is output
to a precoding multiplying section 116.
[0088] The precoding multiplying section 107 shifts the phase
and/or amplitude of the transmission data #k for each of the
reception antennas RX#1 to RX#N based on the precoding weights
obtained from the PMI selected in the PMI selecting section 111.
The transmission data #k with the phase and/or amplitude shifted in
the precoding multiplying section 116 is output to the multiplexer
(MUX) 117.
[0089] The multiplexer (MUX) 117 combines the transmission data #k
with the phase and/or amplitude shifted and the control signal
generated in the feedback control signal generating section 112,
and generates transmission signals for each of the reception
antennas RX#1 to RX#N. The transmission signals generated in the
multiplexer (MUX) 117 are subjected to inverse fast Fourier
transform in inverse fast Fourier transform sections 118#1 to
118#N, transformed from the signals in the frequency domain into
the signals in the time domain, then provided with CPs in CP adding
sections 119#1 to 119#N, and output to RF transmission circuits
120#1 to 120#N. Then, the RF transmission circuits 120#1 to 120#N
perform frequency conversion processing for converting into the
radio frequency band on the signals to output to the reception
antennas RX#1 to RX#N via the duplexers 101#1 to 101#N, and the
signals are transmitted from the reception antennas RX#1 to RX#N to
the radio base station apparatus 20 in uplink.
[0090] In the radio base station apparatus 20 as shown in FIG. 5, a
scheduler, not shown, determines the number of users (the number of
multiplexed users) to multiplex based on channel estimation values
provided from channel estimation sections 215#1 to 215#k, described
later. Then, the scheduler determines the resource allocation
content (scheduling information) of uplink and downlink to each
user, and outputs transmission data #1 to #k to users #1 to #k to
corresponding channel coding sections 201#1 to 201#k.
[0091] The transmission data #1 to #k is subjected to channel
coding in the channel coding sections 201#1 to 201#k, then output
to data modulation sections 202#1 to 202#k, and is subjected to
data modulation. At this point, channel coding and data modulation
is performed based on the channel coding rate and modulation scheme
provided from CQI processing sections 220#1 to 220#k, described
later. The transmission data #1 to #k subjected to data modulation
in the data modulation sections 202#1 to 202#k is subjected to
inverse Fourier transform in a discrete Fourier transform section,
not shown, is transformed from the time-series signal into a signal
in the frequency domain, and is output to a subcarrier mapping
section 203.
[0092] The subcarrier mapping section 203 maps the transmission
data #1 to #k to subcarriers corresponding to scheduling
information provided from the scheduler. At this point, the
subcarrier mapping section 203 maps (multiplexes) reference signals
#1 to #k input from a reference signal generating section, not
shown, to the subcarriers together with the transmission data #1 to
#k. The transmission data #1 to #k thus mapped to the subcarriers
is output to precoding multiplying sections 204#1 to 204#k.
[0093] The precoding multiplying sections 204#1 to 204#k shift the
phases and/or amplitude of the transmission data #1 to #k for each
of transmission antennas TX#1 to TX#N based on the precoding
weights provided from a precoding weight generating section 221,
described later, (weighting of the transmission antennas TX#1 to
TX#N by precoding). The transmission data #1 to #k with the phases
and/or amplitude shifted in the precoding multiplying sections
204#1 to 204#k is output to a multiplexer (MUX) 205.
[0094] The multiplexer (MUX) 205 combines the transmission data #1
to #k with the phases and/or amplitude shifted, and generates
transmission signals for each of the transmission antennas TX#1 to
TX#N. The transmission signals generated in the multiplexer (MUX)
205 are subjected to inverse fast Fourier transform in inverse fast
Fourier transform sections 206#1 to 206#N, and are transformed from
the signals in the frequency domain into the signals in the time
domain. Then, the signals are provided with CPs in cyclic prefix
(CP) adding sections 207#1 to 207#N, and are output to RF
transmission circuits 208#1 to 208#N. Then, the RF transmission
circuits 208#1 to 208#N perform frequency conversion processing for
converting into the radio frequency band on the signals to output
to the transmission antennas TX#1 to TX#N via the duplexers 209#1
to 209#N, and the signals are transmitted from the transmission
antennas TX#1 to TX#N to the mobile station apparatuses 10 in
downlink.
[0095] Meanwhile, transmission signals transmitted from the mobile
station apparatuses 10 in uplink are received in the transmission
antennas TX#1 to TX#N, electrically divided into transmission paths
and reception paths in the duplexers 209#1 to 209#N, and then,
output to RF reception circuits 210#1 to 210#N. Then, the signals
undergo frequency conversion processing for converting a
radio-frequency signal into a baseband signal in the RF reception
circuits 210#1 to 210#N. CPs are removed from the baseband signals
subjected to the frequency conversion processing in CP removing
sections 211#1 to 211#N, and the resultants are output to Fast
Fourier Transform sections (FFT sections) 212#1 to 212#N. A
reception timing estimation section 213 estimates reception timing
from reference signals included in the reception signals, and
notifies the CP removing sections 211#1 to 211#N of the estimation
result. The FFT sections 212#1 to 212#N perform Fourier transform
on the input reception signals, and transform the time-series
signals into signals in the frequency domain. The reception signals
transformed into the signals in the frequency domain are output to
data channel signal dividing sections 214#1 to 214#k.
[0096] The data channel signal dividing sections 214#1 to 214#k
divide the reception signals input from the FFT sections 212#1 to
212#k, for example, by Minimum Mean Square Error (MMSE) or Maximum
Likelihood Detection (MLD) signal division method. By this means,
the reception signals coming from the mobile station apparatuses 10
are divided into reception signals concerning users #1 to #k. The
channel estimation sections 215#1 to 215#k estimate channel states
from reference signals included in the reception signals output
from the FFT sections 212#1 to 212#k, and notify the estimated
channel states to the data channel signal dividing sections 214#1
to 214#k, and control channel signal demodulation sections 216#1 to
216#k. The data channel signal dividing sections 214#1 to 214#k
divide the reception signals by the above-mentioned MLD signal
division method based on the notified channel states.
[0097] The reception signals concerning the users #1 to #k divided
in the data channel signal dividing sections 214#1 to 214#k are
demapped in subcarrier demapping sections, not shown, restored to
the time-series signals, and then, are subjected to data
demodulation in data demodulation sections, not shown. Then,
channel decoding sections 217#1 to 217#k perform channel decoding
processing, and transmission signals #1 to #k are thus
reproduced.
[0098] The control channel signal demodulation sections 216#1 to
216#k demodulate control channel signals (for example, PDCCHs)
included in the reception signals input from the FFT sections 212#1
to 212#k. At this point, the control channel signal demodulation
sections 216#1 to 216#k demodulate control channel signals
respectively associated with the users #1 to #k. At this point, the
control channel signal demodulation sections 216#1 to 216#k
demodulate the control channel signals based on the channel states
notified from the channel estimation sections 215#1 to 215#k. The
control channel signals demodulated in the control channel signal
demodulation sections 216#1 to 216#k are output to PMI processing
sections 218#1 to 218#k, IQI processing sections 219#1 to 219#k,
and CQI processing sections 219#1 to 219#k, respectively.
[0099] The PMI processing sections 218#1 to 218#k extract PMIs from
the information included in respective control channel signals (for
example, PUCCHs) input from the control channel signal demodulation
sections 216#1 to 216#k. The PMIs reproduced in the PMI processing
sections 218#1 to 218#k are output to a precoding weight generating
section 221.
[0100] The IQI processing sections 219#1 to 219#k extract the IQIs
or IQI.sub.i,UE.sup.j from the information included in respective
control channel signals (for example, PUCCHs) input from the
control channel signal demodulation sections 216#1 to 216#k.
Further, in the above-mentioned first feedback information, each of
the IQI processing sections 219#1 to 219#k outputs the extracted
IQI to the precoding weight generating section 221. In the
above-mentioned second feedback information, each of the IQI
processing sections 219#1 to 219#k obtains the IQI using
information (parameters included in above-mentioned equations (5),
(7), (9), (10) and (11)) necessary for IQI measurement including at
least the channel estimation value and PMI from the mobile terminal
apparatus (UE). In other words, each of the IQI processing sections
219#1 to 219#k calculates the IQI using extracted
IQI.sub.i,UE.sup.j by above-mentioned equation (5), (7), (9), (10)
or (11), and outputs the IQI to the precoding weight generating
section 221.
[0101] In the latter case, for example, in Aspect 1, each of the
IQI processing sections 219#1 to 219#k calculates the IQI of the
connected cell and the IQI of the coordinated cell by
above-mentioned equation (5) or (7). Further, in Aspect 2, each
section calculates the IQI of the connected cell and the IQI of the
coordinated cell by above-mentioned equation (9). In Aspect 3, each
section calculates the IQI of the connected cell and the IQI of the
coordinated cell by above-mentioned equation (10). Further, when
necessary, each of the IQI processing sections 219#1 to 219#k
time-averages the IQI by above-mentioned equation (15) or (16).
[0102] The CQI processing sections 220#1 to 220#k measure CQIs from
the reference signals included in respective control channel
signals (for example, PUCCHs) input from the control channel signal
demodulation sections 216#1 to 216#k, while always updating the CQI
information to the latest state. The CQI information updated in the
CQI processing sections 219#1 to 219#k is output to the channel
coding sections 201#1 to 201#k and data modulation sections 202#1
to 202#k, respectively.
[0103] The precoding weight generating section 221 generates
precoding weights indicative of the phase and/or amplitude shift
amounts for the transmission data #1 to #k, using the PMIs input
from the PMI processing sections 218#1 to 218#k, and the IQIs input
from the IQI processing sections 219#1 to 219#k. The generated
precoding weights are output to the precoding multiplying sections
204#1 to 204#k, and used in precoding of the transmission data #1
to #k.
[0104] The precoding weight generating section 220 generates
precoding weights as described below. First, as shown in following
equation (17), the section 220 makes the PMIs channel coefficients
(in the case based on the premise that the number of radio base
station apparatuses in the coordinated cluster is "3" and that the
number of reception antennas on the mobile terminal side is "2").
Eq. (17)
H.sub.i.sup.1=(F.sub.i.sup.1).sup.H,H.sub.i.sup.2=(F.sub.i.sup.2).sup.H,-
H.sub.i.sup.3=(F.sub.i.sup.3).sup.H
[0105] Next, from the channel coefficients and IQIs obtained in
equation (17), the section 220 obtains channel covariance matrixes
of the connected cell (eNB.sub.1 in FIG. 1) and coordinated cell
(eNB.sub.2 in FIG. 1) by following equation (18).
(Serving cell)
{circumflex over
(R)}.sub.i=H.sub.i.sup.i.times.[.sup.IQI.sup.i.sup.i.sub.IQI.sub.i.sub.i]-
.times.(H.sub.i.sup.i).sup.H
(Coordinating cell)
{circumflex over
(R)}.sub.j=H.sub.j.sup.i.times.[.sup.IQI.sup.i.sup.i.sub.IQI.sub.i.sub.i]-
.times.(H.sub.j.sup.i).sup.H{circumflex over
(R)}.sub.k=H.sub.k.sup.i.times.[.sup.IQI.sup.i.sup.i.sub.IQI.sub.i.sub.i]-
.times.(H.sub.k.sup.i).sup.H Eq. (18)
[0106] Subsequently, the section 220 obtains precoding weights in
SLNR precoding from the channel covariance matrixes of the
connected cell and coordinated cell by following equation (19). Eq.
(19)
P.sub.i=max eigenvector[(I+{circumflex over (R)}.sub.j+{circumflex
over (R)}.sub.k).sup.-1{circumflex over (R)}.sub.i]
(First Feedback Method)
[0107] In the mobile communication system having the
above-mentioned configuration, in the mobile terminal apparatus
(UE), the channel estimation section 107 performs channel
estimation using downlink reference signals. Then, the PMI
selecting section 111 selects the PMI using the channel estimation
values obtained in the channel estimation section 107. Next, the
IQI measuring section 109 measures the IQI using at least the
channel estimation values and PMI. At this point, the IQI measuring
section 109 calculates the IQI by equation (5), (7), (9), (10) or
(11) according to any one of above-mentioned Aspects 1 to 3. The
IQI is transmitted to the radio base station apparatus eNB as
feedback.
[0108] In the radio base station apparatus eNB, the precoding
weight generating section 221 generates precoding weights using the
PMIs and IQIs transmitted as feedback. At this point, the precoding
weight generating section 221 generates precoding weights by
above-mentioned equations (17) to (19). Next, the radio base
station apparatus eNB performs coordinated multipoint transmission
utilizing MIMO transmission, using the obtained precoding
weights.
(Second Feedback Method)
[0109] In the mobile communication system having the
above-mentioned configuration, in the mobile terminal apparatus
(UE), the channel estimation section 107 performs channel
estimation using downlink reference signals. Then, the PMI
selecting section 111 selects the PMI using the channel estimation
values obtained in the channel estimation section 107. Next, the
IQI measuring section 109 calculates the IQI.sub.i,UE.sup.j using
at least the channel estimation values and PMI. At this point, the
IQI measuring section 109 calculates the IQI.sub.i,UE.sup.j by
equation (5), (7), (9), (10) or (11) according to any one of
above-mentioned Aspects 1 to 3. The IQI.sub.i,UE.sup.j is
transmitted to the radio base station apparatus eNB as
feedback.
[0110] In the radio base station apparatus eNB, the IQI processing
section 219 calculates the IQI using the IQI.sub.i,UE.sup.j. At
this point, the IQI processing section 219 calculates the IQI by
equation (5), (7), (9), (10) or (11) according to any one of
above-mentioned Aspects 1 to 3. Next, the precoding weight
generating section 221 generates precoding weights using the PMIs
transmitted as feedback and calculated IQIs. At this point, the
precoding weight generating section 221 generates precoding weights
by above-mentioned equations (17) to (19). Next, the radio base
station apparatus eNB performs coordinated multipoint transmission
utilizing MIMO transmission, using the obtained precoding
weights.
[0111] In the above-mentioned descriptions, the present invention
is specifically described using the above-mentioned Embodiment, but
it is obvious to a person skilled in the art that the invention is
not limited to the Embodiment described in the Description. The
invention is capable of being carried into practice as modified and
changed aspects without departing from the subject matter and scope
of the invention defined by the descriptions of the scope of the
claims. Accordingly, the descriptions of the Description are
intended for illustrative explanation, and do not have any
restrictive meaning to the invention.
[0112] The present application is based on Japanese Patent
Application No. 2011-047972 filed on Mar. 4, 2011, entire content
of which is expressly incorporated by reference herein.
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